I'll bite. 2 km/s is a measure of escape velocity, which seems to be a reasonable way to quantify the depth of a gravity well, but I'm not qualified to say whether it's a more or less useful measurement than the gravitational acceleration.
What did you expect, really? Why would Blizzard alienate all the fans of the first game by completely changing it up?
On the flip side, I can say that if you've played SC1 and enjoyed it, you'll probably enjoy SC2 as well. In fact, there are a bunch of little improvements (rally workers to resources, idle worker button, select more than 12 units at once, better pathing, etc.) that make 2 much less of a hassle at times than 1.